The research and development of the combustion of hydrogen or hydrogen-rich fuels in gas turbines involves at least two factors:
On the one hand, there is a global interest in reducing the emission of greenhouse gases, especially of CO2. One possibility for this is the changeover from fossil fuels to a hydrogen-based energy supply. In this case, this can be based on fossil raw materials with hydrogen synthesis and CO2 bonding.
On the other hand, limited natural gas reserves have led to considerations of using synthetically processed gaseous fuels alternatively to, or in combination with, the combustion of conventional types of fuel. These synthetically processed gaseous fuels, as are found for example in an IGCC (Integrated Gasification Combined Cycle), which can contain high hydrogen concentrations.
The combustion of hydrogen in known combustion systems of gas turbines can lead to, for example, flashback and increased NOx emissions, on account of the high flame velocity and short ignition delay time of the hydrogen.
As countermeasures, in addition to the simple reduction of the operating values, the possibility of diluting the hydrogen-rich fuel with N2 or other inert gases, and different concepts for the dilution of the combustion air or of the fuel gas with steam, are known. For example, steam is injected, or water is injected for evaporation in the air passage or in the fuel system.
For reduction of the NOx emissions, widely different possibilities for “mild combustion” or “flameless combustion” are known from literature. In this case, by recirculation of some of the flue gases, the oxygen concentration of the combustion air can be reduced. For this purpose, in DE10297365 it is proposed to recirculate some of the combustion air around the combustion chamber before expansion in the turbine and to mix it with the compressor exit air.
DE19810820 addresses increased NOx emissions when combusting nitrogenous fuels, such as occur for example when combusting ammoniacal fuel gases. For the reduction of this so-called “fuel NOx”, it is proposed to further cool the flue gases after discharging from the turbine and to admix them in the inlet of the compressor or to compress them in a separate flue-gas compressor and to admix them at the inlet of the combustion chamber in order to find a minimum of NOx emissions in the case of an oxygen content of, for example, 14% to 16%.
The disclosures of DE10297365 and DE19810820 are hereby incorporated by reference in their entireties.
Flue gas recirculation is further known to increase the concentration of CO2 in the flue gas and at the same time to reduce the discharging amount of flue gas and consequently to reduce the cost for CO2 extraction from the flue gases (P. Chiesa, S. Consonni: Natural Gas Fired Combined Cycles with Low
CO2 Emissions, Journal of Engineering for Gas Turbines and Power, Vol. 122, ASME, July 2000, p. 429-436, the disclosure of which is hereby incorporated by reference in its entirety).
A particular form of the flue gas recirculation is a recirculation of some of the flue gas in, and mixing with, the fuel gas. This form of flue gas recirculation into the fuel gas is known from U.S. Pat. No. 5,595,059, the disclosure of which is hereby incorporated by reference in its entirety. There, the flue gas is compressed by an flue gas compressor after discharging from a device for utilizing the waste heat which is connected downstream to the gas turbine installation. The compressed flue gas is mixed with fuel gas and fed to a reformer before the reformed gas is introduced into the combustion chamber.